All digital implementation of clock spectrum spreading (dither) for low power/die area

ABSTRACT

A digital circuit configured to spread a clock train spectrum includes a clock configured to generate the clock train, and a variable divider configured to divide the frequency of the clock train by a temporally-varying-divider value to modulate the clock train and generate a dithered clock train. The circuit further includes a first accumulator configured to accumulate the dithered clock train to generate a frequency modulation waveform, and a second accumulator configured accumulate the frequency modulated waveform to generate a phase modulation signal. The circuit further includes a phase-value calculator configured to calculate the temporally-varying divider value based on the phase modulation signal; and a closed-loop control circuit configured to track and filter the modulation of the dithered clock train to generate a second clock train that is the spread spectrum of the first mentioned clock train.

RELATED APPLICATIONS

This application is a continuation of co-pending U.S. application Ser.No. 11/246,328, filed Oct. 6, 2005, which claims the benefit of U.S.Provisional Application No. 60/704,510, filed Aug. 1, 2005, and U.S.Provisional Application No. 60/722,731, filed Sep. 30, 2005, all ofwhich are incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to integrated circuits, and moreparticularly relates to digitally spreading a clock spectrum in digitalcircuits.

The spreading of a clock spectrum generally includes spreading the powerof clock pulses over a range of frequencies. FIG. 1 is a simplifiedschematic of a first clock train 100 and a spread-spectrum clock train105. The pulses in spread-spectrum clock train 105 are spread-spectrumpulses that may be generated from the clock pulses in the first clocktrain 100. The clock edges of the spread-spectrum pulses move in and outas indicated by the arrows in FIG. 1. A spread-spectrum clock train istypically generated for applications in which jitter sensitivity isgenerally low and/or in which lowering peak power of clock pulses isdesired.

Traditional circuits configured to spread the spectrum of a clock trainoften include both digital and analog circuits, which typically includea digital modulator and an analog phase interpolator. The digitalmodulator is configured to receive a clock train (e.g., the first clocktrain) from a clock generator. The clock train may be a digital clocktrain. The digital modulator may be configured to modulate the clocktrain using a dithering waveform to generate a dithered waveform. Thedithered waveform may then be transferred to the analog-phaseinterpolator that is configured to phase interpolate the ditheredwaveform. Based on the phase interpolation of the dithered waveform, theanalog-phase interpolator is configured to generate and output aspread-spectrum clock train.

These traditional circuits configured to spread the spectrum of a clocktrain have a number of inherent shortcomings especially for low powercircuit applications. For example, typical digital modulators configuredto modulate a clock train typically operate at the clock frequency ofthe clock train, which is typically the relatively high frequency of afree running clock (e.g., generated by a crystal oscillator). Astraditional digital modulators are configured to operate at a freerunning clock frequency, these digital modulators tend to drawrelatively high current.

Not only do the digital modulators included in these traditionalcircuits typically draw relatively high current, the analog-phaseinterpolators in these traditional circuits also typically drawrelatively high current. For example, an analog-phase interpolator maydraw as much as a digital modulator. Moreover, as these traditionalcircuits typically include analog devices (namely, an analog-phaseinterpolator), the shape of the spread-spectrum clock pulses and theamount of power reduction of these clock pulses is generally limited bythe linearity of the analog-phase interpolator. Analog-phaseinterpolators having relatively high linearly are relatively costly todesign and manufacture, and are relatively large. Also, as thesetraditional circuits often include both digital circuits and analogcircuits, these traditional circuits tend to take up relatively largeamounts of die space, which tends to make these circuits relativelycostly to manufacture.

Therefore, new circuits are needed that are configured to spread thespectrum of a clock train, that draw relatively less current thantraditional circuits that are configured to provide this function, andthat take up relatively less die area than traditional circuits.

BRIEF SUMMARY

Accordingly, embodiments of the present invention provide circuits,methods, apparatus, code for controlling circuits, code, and/or means tocondition a clock train, and specifically to spread the spectrum of theclock train.

According to an exemplary embodiment of the present invention, codeconfigured to spread the spectrum of a clock train includes code forgenerating the clock train, and code for dividing the frequency of theclock train by a temporally-varying-divider value to modulate the clocktrain and generate a dithered clock train. The exemplary embodimentfurther includes code for accumulating the dithered clock train togenerate a frequency modulation waveform; and code for accumulating thefrequency modulated waveform to generate a phase modulation signal. Theexemplary embodiment further includes code for calculating thetemporally-varying divider value based on the phase modulation signal;and code for tracking and filtering the modulation of the dithered clocktrain to generate a second clock train.

According to a specific embodiment of the code, the first clock train isa digital clock train. The temporally-varying divider value is afixed-divider value plus a phase value. The phase value is determinedfrom the frequency modulation waveforn. The phase value is proportionalto the deviation of the frequency modulation waveform from the center ofthe frequency modulation waveform. The frequency modulation waveform isperiodic or quasi-periodic. The frequency modulation waveform is atriangle waveform. The closed-loop control circuit is configured tomultiply the frequency of the dithered clock train by a fixed-multipliervalue. The temporally-varying divider value is a fixed-divider valueplus a phase value, and the average frequency of the second clock trainis the frequency of the first clock train multiplied by thefixed-multiplier value and divided by the fixed-divider value. Theexemplary embodiment further includes code for calculating thedifference between a first portion of the phase modulation signal and asecond portion of the phase modulation signal, wherein the secondportion is temporally retarded with respect to the first portion; andthe difference is the phase value. The exemplary embodiment furtherincludes code for adding the phase value to a fixed divider value togenerate the temporally-varying-divider value.

Another exemplary embodiment of the present invention includes means forspreading the spectrum of a clock train, and more specifically includesclock generating means for generating the clock train, and a variabledivider means for receiving the clock train from the clock generatormean and dividing the frequency of the clock train by atemporally-varying-divider value to modulate the clock train andgenerate a dithered clock train. The exemplary embodiment furtherincludes first accumulator means for receiving the dithered clock trainfrom the variable divider means and accumulating the dithered clocktrain to generate a frequency modulation waveform. The exemplaryembodiment further includes second accumulator means for receiving thefrequency modulation waveform from the first accumulator means andaccumulating the frequency modulated waveform to generate a phasemodulation signal. The exemplary embodiment further includes phase-valuecalculator means for receiving the phase modulation signal from thesecond accumulator means and calculating the temporally-varying dividervalue based on the phase modulation signal. The exemplary embodimentfurther includes closed-loop control means for receiving the ditheredclock train from the variable divider means and tracking and filteringthe modulation of the dithered clock train to generate a second clocktrain that is the spread spectrum of the first mentioned clock train.

According to a specific embodiment of the clock spreading means, thefirst clock train is a digital clock train. The temporally-varyingdivider value is a fixed-divider value plus a phase value. The phasevalue is determined from the frequency modulation waveform. The phasevalue is proportional to the deviation of the frequency modulationwaveform from the center of the frequency modulation waveform. Thefrequency modulation waveform is periodic or quasi-periodic. Thefrequency modulation waveform is a triangle waveform. The clock pulsesof the second clock train have larger temporal widths than the clockpulses of the first clock train. The closed-loop control means isconfigured for multiplying the frequency of the dithered clock train bya fixed-multiplier value. The temporally-varying divider value is afixed-divider value plus a phase value, and the average frequency of thesecond clock train is the frequency of the first clock train multipliedby the fixed-multiplier value and divided by the fixed-divider value.The exemplary embodiment further includes means for calculating thedifference between a first portion of the phase modulation signal and asecond portion of the phase modulation signal, wherein the secondportion is temporally retarded with respect to the first portion; andthe difference is the phase value. The exemplary embodiment furtherincludes means for adding the phase value to a fixed divider value togenerate the temporally-varying-divider value.

Another exemplary embodiment of the present invention includes code forspreading a clock spectrum, and more specifically includes code forgenerating a phase value based on a frequency modulation waveform; andcode for dividing a frequency of the clock train by a divider value thatincludes a fixed value plus the phase value to generate a dithered clocktrain that is phase modulated by the phase value. The exemplaryembodiment further includes code for accumulating the dithered clocktrain to generate the frequency modulation waveform; and code foraccumulating the frequency modulation waveform to generate a phasemodulation signal and generate the phase value based on the phasemodulation signal. The exemplary embodiment further includes code fortracking and locking onto the modulation of the dithered clock train;and based on the tracking and locking steps, code for generating aspread-spectrum clock train that is the spread spectrum of the clocktrain. The frequency modulation waveform is periodic or quasi periodic.The frequency modulation waveform is a triangle waveform. The frequencymodulation waveform is a digital signal. The clock train is a digitalclock train. The dithered clock train is a digital clock train. Thephase value is proportional to the deviation of the frequency modulationwaveform from the center of the frequency modulation waveform. Theexemplary embodiment further includes code for multiplying the frequencyof the dithered clock train by a multiplier value. The average frequencyof the spread-spectrum clock train is the frequency of the clock trainmultiplied by the multiplier value divided by the fixed value. Theexemplary embodiment further includes code for splitting the phasemodulation signal into a first phase modulation signal and a secondphase modulation signal; code for temporally delaying the second phasemodulation signal with respect to the first phase modulation signal; andcode for thereafter calculating the different between the first phasemodulation signal and the second phase modulation signal to generate thephase value. The exemplary embodiment further includes code for addingthe phase value to the fixed value to generate the divider value.

Another exemplary embodiment of the present invention includes means forspreading a clock spectrum, and more specifically includes means forgenerating a phase value based on a frequency modulation waveform; andmeans for dividing a frequency of the clock train by a divider valuethat includes a fixed value plus the phase value to generate a ditheredclock train that is phase modulated by the phase value. The exemplaryembodiment further includes means for accumulating the dithered clocktrain to generate the frequency modulation waveform; and means foraccumulating the frequency modulation waveform to generate a phasemodulation signal and generate the phase value based on the phasemodulation signal. The exemplary embodiment further includes means fortracking and locking onto the modulation of the dithered clock train.The exemplary embodiment further includes means for generating aspread-spectrum clock train that is the spread spectrum of the clocktrain based on tracking the modulation of the dithered clock train andfiltering the dithered clock train. The frequency modulation waveform isperiodic or quasi periodic. The frequency modulation waveform is atriangle waveform. The frequency modulation waveform is a digitalsignal. The clock train is a digital clock train. The dithered clocktrain is a digital clock train. The phase value is proportional to thedeviation of the frequency modulation waveform from the center of thefrequency modulation waveform. The exemplary embodiment further includesmeans for multiplying the frequency of the dithered clock train by amultiplier value. The average frequency of the spread-spectrum clocktrain is the frequency of the clock train multiplied by the multipliervalue divided by the fixed value. The exemplary embodiment furtherincludes means for splitting the phase modulation signal into a firstphase modulation signal and a second phase modulation signal; means fortemporally delaying the second phase modulation signal with respect tothe first phase modulation signal; and means for thereafter calculatingthe different between the first phase modulation signal and the secondphase modulation signal to generate the phase value. The exemplaryembodiment further includes means for adding the phase value to thefixed value to generate the divider value.

Another exemplary embodiment of the present invention includes code forspreading the spectrum of a clock train, and more specifically includescode for generating a dithered clock train, and code for accumulatingthe dithered clock train to generate a frequency modulation waveform.The exemplary embodiment further includes code for accumulating thefrequency modulation waveform to generate a phase modulation signal; andcode for generating a temporally-varying divider value based on thephase modulation signal. The exemplary embodiment further includes codefor digitally modulating the width based on the temporally-varyingdivider value. The exemplary embodiment further include code fortracking the modulation of the dithered clock train and filtering thedithered clock train to generate a second clock train that is the spreadspectrum of the first mentioned clock train. The temporally-varyingdivider value is a fixed-divider value plus a phase value. The exemplaryembodiment further includes code for generating the phase value based onthe phase modulation signal. The exemplary embodiment further includescode for splitting the phase modulation signal into first and secondphase modulation signals; and code for delaying the second phasemodulation signal with respect to the first modulation signal tothereafter calculate the difference between first phase modulationsignal and the second phase modulation signal to generate the phasevalue. The exemplary embodiment further includes code for adding thephase value to the fixed-divider value. The phase value is proportionalto the deviation of the digital-frequency modulation waveform from thecenter of the digital-frequency modulation waveform. The frequencymodulation waveform is a periodic or quasi-periodic. The frequencymodulation waveform is a triangle waveform.

Another exemplary embodiment of the present invention includes means forspreading the spectrum of a clock train, and more specifically includesmeans for generating a dithered clock train, and means for accumulatingthe dithered clock train to generate a frequency modulation waveforn.The exemplary embodiment further includes means for accumulating thefrequency modulation waveform to generate a phase modulation signal; andmeans for generating a temporally-varying divider value based on thephase modulation signal. The exemplary embodiment further includes meansfor digitally modulating the clock train based on the temporally-varyingdivider value. The exemplary embodiment further include means fortracking the modulation of the dithered clock train and filtering thedithered clock train to generate a second clock train that is the spreadspectrum of the first mentioned clock train. The temporally-varyingdivider value is a fixed-divider value plus a phase value. The exemplaryembodiment further includes means for generating the phase value basedon the phase modulation signal. The exemplary embodiment furtherincludes means for splitting the phase modulation signal into first andsecond phase modulation signals; and means for delaying the second phasemodulation signal with respect to the first modulation signal tothereafter calculate the difference between first phase modulationsignal and the second phase modulation signal to generate the phasevalue. The exemplary embodiment further includes means for adding thephase value to the fixed-divider value. The phase value is proportionalto the deviation of the digital-frequency modulation waveform from thecenter of the digital-frequency modulation waveform. The frequencymodulation waveform is a periodic or quasi-periodic. The frequencymodulation waveform is a triangle waveform.

A better understanding of the nature and advantages of the presentinvention may be gained with reference to the following detaileddescription and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic of a first clock train and aspread-spectrum clock train that may be generated from the first clocktrain according to one embodiment of the present invention;

FIG. 2 is a simplified schematic of a digital circuit configured togenerate a spread-spectrum clock train according to one embodiment ofthe present invention;

FIG. 3 is a high-level flow chart having steps for generating aspread-spectrum clock train according to one embodiment of the presentinvention; and

FIGS. 4A-4H illustrate various implementations of exemplary embodimentsof the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present invention generally provides a digital circuit apparatus anddigital circuit method for conditioning a digital signal. Morespecifically, the present invention provides a digital circuit apparatusand digital circuit method for spreading a clock spectrum.

Spreading a clock spectrum, such as a digital clock spectrum, includesspreading the power of clock pulses over a range of frequencies. FIG. 1is a simplified schematic of a first clock train 100 and aspread-spectrum clock train 105 that may be generated from the firstclock train according to an embodiment of the present invention. Theedges of the spread-spectrum clock train are dithered with respect tothe first clock train as indicated by the arrows in FIG. 1. The clockpulses of the first clock train may be digitally conditioned to generatethe spread spectrum clock pulses in the spread-spectrum clock train.

FIG. 2 is a simplified schematic of a circuit 200 according to oneembodiment of the present invention. Circuit 200 includes a clock pulsegenerator 205, a variable divider 210, a first accumulator 215, a secondaccumulator 220, a delay circuit 225, and first adder 230, a secondadder 235, and a phase-locked loop (PLL) 240. Delay circuit 225, adder230, and adder 235 are sometimes referred to herein as the phase-valuecalculator. According to one embodiment, each of the forgoing listedcircuits is a digital circuit. According to an alternative embodiment,the PLL may be a mixed signal circuit. Circuit 200 is configured togenerate the first clock train 100, and condition the first clock trainto generate the spread-spectrum clock train 105. The frequency “f1” ofthe first clock train may be the oscillation frequency of a free runningclock, such as a crystal oscillator. The average frequency “f2” of thespread-spectrum clock train can be less than, equal to, or greater thanto f1.

According to one embodiment, clock pulse generator 205 is configured togenerate the first clock train 100, which may be a digital clock train.The first clock train is transferred from an output of clock pulsegenerator 205 to an input of variable divider 210. Variable divider 210is configured to generate a dithered clock train 245 that has afrequency “f3.” More specifically, the variable divider is configured todivide the frequency f1 of the clock train by a “divider” value N+δ,wherein f3 is equal to f1/(N+δ). N may be a fixed value (e.g., 128) andδ may be a time varying value (referred to herein as a phase value).Generation of the phase value is described in detail below. The phasevalue may be relatively small compared to the N. For example, theabsolute value of δ may be 10 times less than N, or smaller (e.g., 20times less than N). The value of N may be user specified or may bespecified by other circuits (not shown) that are coupled to circuit 200.The value of N may be specified according to a particular applicationfor which circuit 200 is intended.

Dithered clock train 245 may be transferred from an output of thevariable divider to an input of accumulator 215 and to an input of PLL240. Accumulator 215 (sometimes referred to herein as a frequencyaccumulator) is configured to accumulate the dithered clock train, andtherefrom, generate a frequency modulation waveform 250, which may be adigital signal. The frequency modulation waveform may be periodic orquasi periodic and may have a variety of shapes, such as triangular,saw-toothed, teardrop, capricious or the like. The frequency modulationwaveform is used by circuit 200 to modulate the phase of clock train 100to generate the dithered clock train having dithered edges.Specifically, the frequency modulation waveform is transferred from anoutput of accumulator 215 to an input of accumulator 220 (sometimesreferred to herein as the phase accumulator). Accumulator 220 isconfigured to accumulate the frequency modulation waveform and isconfigured to receive the dithered clock train from the variabledivider. Accumulator 220 is further configured to generate a phasemodulation signal 255 from the accumulated frequency modulationwaveform.

According to one embodiment, the phase value is proportional to thedeviation of the frequency modulation waveform from the center of thefrequency modulation waveform. For example, if the frequency modulationwaveform is a triangle waveform, the phase value may be proportional toa value of the triangle waveform above or below a reference line 260.More specifically, to calculate the phase value, the phase modulationsignal is transferred via two circuit paths 265 a and 265 b to adder230. Circuit path 265 a might be a non-delayed path. Circuit path 265 bmay include delay circuit 225 that is configured to delay the phasemodulation signal in the second circuit path relative to the phasemodulation signal in the first circuit path. Delay circuit 225 may delaythe phase modulation signal in circuit path 265 b based on the receiveddithered clock 245. Adder 230 is configured to subtract the delayedphase modulation signal from the phase modulation signal that is notdelayed. Stated alternatively, adder 230 is configured to calculate thedifference in the phase modulation signal at different “time points.”The calculated difference in the phase modulation signal at differenttime points is the phase value δ. The phase value δ is transferred fromadder 230 to adder 235, which is configured to add the phase value tothe fixed value N to generate the divider value N+δ. δ may be negativeor positive depending, for example, on the amount the phase modulationsignal is delayed by the delay circuit.

As the frequency modulation waveform changes with time, so too does thephase value. For example, as the frequency modulation waveform rises,the phase value similarly rises, and as the frequency modulationwaveform decreases, the phase value similarly decreases. The phase valuemay decrease from a positive value to a negative value as the phasemodulation waveform changes. Further, as the phase value changes withtime, so too does the divider value N+δ. Further yet, as the dividervalue temporally changes, the variable divider divides the frequency f1of the first clock train by these temporally changing divider values.For example, as the divider values increase, the edges of the ditheredclock train generated by the variable divider extend (i.e., thefrequency of the dithered clock train decreases), and as the dividervalues decrease, the edges of the dithered clock train retract (i.e.,the frequency of the dithered clock train increases). This phase changeof the dithered clock train changes at approximately the frequency ofthe frequency modulation waveform.

According to one embodiment, the frequency of the phase change of thedithered clock train is within the operable detection range of PLL 240.Accordingly, the PLL can track and lock onto the modulation of thedithered clock train to filter the dithered clock train to generate thespread-spectrum clock train. As the edges (i.e., phase) of the ditheredclock train dither, the edges of the clock pulses of the spread-spectrumclock train similarly dither.

According to one embodiment, the PLL may be configured to multiply thefrequency of the dithered clock train by a multiplier value “M,” suchthat the average frequency f2 of spread-spectrum clock train 105 is(M/N)·f1. The value of M may be adjusted to tune the frequency f2 to avariety of desired values.

FIG. 3 is a high-level flow chart having steps for spreading thespectrum of clock pulses composing clock train 100 to generatespread-spectrum clock train 105. It should be understood that the stepsof the described high-level flow are exemplary and that various stepsmay be substituted with alternative steps, steps may be combined, and/orsteps may be eliminated without deviation from the embodimentrepresented by the high-level flow chart. In an initial step 300, thevariable divider receives the clock train and the temporally-varyingdivider value. In a step 305, the variable divider divides the frequencyof the clock train by the temporally-varying divider value to phasemodulate the clock train and thereby generate the dithered clock train.The temporally-varying divider value includes the fixed value plus thephase value, which temporally varies. In a step 310, the frequencyaccumulator receives the dithered clock train from the variable divider,and generates the frequency modulation waveform based on accumulation ofthe dithered clock train. In a step 315, the phase accumulator receivesthe frequency modulation waveform from the frequency accumulator andgenerates the phase modulation signal based on accumulation of thefrequency modulation waveform. In a step 320, the phase-value calculatorcalculates the difference between different time points of the phasemodulation signal; the difference is the phase value. In a step 325, thephase value is added to the fixed value to generate thetemporally-varying divider value. In a step 330, a phase-locked loop(PLL) receives the dithered clock train from the variable divider. In astep 335, the PLL tracks the modulation of the dithered clock train andfilters the dithered clock train to generate and output thespread-spectrum clock train.

Referring now to FIGS. 4A-4G, various exemplary implementations of thepresent invention are shown. Referring to FIG. 4A, the present inventionmay be embodied in a hard disk drive 400. The present invention mayimplement either or both signal processing and/or control circuits,which are generally identified in FIG. 4A at 402. In someimplementations, signal processing and/or control circuit 402 and/orother circuits (not shown) in HDD 400 may process data, perform codingand/or encryption, perform calculations, and/or format data that isoutput to and/or received from a magnetic storage medium 406.

HDD 400 may communicate with a host device (not shown) such as acomputer, mobile computing devices such as personal digital assistants,cellular phones, media or MP3 players and the like, and/or other devicesvia one or more wired or wireless communication links 408. HDD 400 maybe connected to memory 409, such as random access memory (RAM), a lowlatency nonvolatile memory such as flash memory, read only memory (ROM)and/or other suitable electronic data storage.

Referring now to FIG. 4B, the present invention may be embodied in adigital versatile disc (DVD) drive 410. The present invention mayimplement either or both signal processing and/or control circuits,which are generally identified in FIG. 4B at 412, and/or mass datastorage 418 of DVD drive 410. Signal processing and/or control circuit412 and/or other circuits (not shown) in DVD 410 may process data,perform coding and/or encryption, perform calculations, and/or formatdata that is read from and/or data written to an optical storage medium416. In some implementations, signal processing and/or control circuit412 and/or other circuits (not shown) in DVD 410 can also perform otherfunctions such as encoding and/or decoding and/or any other signalprocessing functions associated with a DVD drive.

DVD drive 410 may communicate with an output device (not shown) such asa computer, television or other device via one or more wired or wirelesscommunication links 417. DVD 410 may communicate with mass data storage418 that stores data in a nonvolatile manner. Mass data storage 418 mayinclude a hard disk drive (HDD) such as that shown in FIG. 4A. The HDDmay be a mini HDD that includes one or more platters having a diameterthat is smaller than approximately 1.8″. DVD 410 may be connected tomemory 419, such as RAM, ROM, low latency nonvolatile memory such asflash memory, and/or other suitable electronic data storage.

Referring now to FIG. 4C, the present invention may be embodied in ahigh definition television (HDTV) 420. The present invention mayimplement either or both signal processing and/or control circuits,which are generally identified in FIG. 4C at 422, a WLAN interfaceand/or mass data storage of the HDTV 420. HDTV 420 receives HDTV inputsignals in either a wired or wireless format and generates HDTV outputsignals for a display 426. In some implementations, signal processingcircuit and/or control circuit 422 and/or other circuits (not shown) ofHDTV 420 may process data, perform coding and/or encryption, performcalculations, format data and/or perform any other type of HDTVprocessing that may be required.

HDTV 420 may communicate with mass data storage 427 that stores data ina nonvolatile manner such as optical and/or magnetic storage devices. Atleast one HDD may have the configuration shown in FIG. 4A and/or atleast one DVD may have the configuration shown in FIG. 4B. The HDD maybe a mini HDD that includes one or more platters having a diameter thatis smaller than approximately 1.8″. HDTV 420 may be connected to memory428 such as RAM, ROM, low latency nonvolatile memory such as flashmemory and/or other suitable electronic data storage. HDTV 420 also maysupport connections with a WLAN via a WLAN network interface 429.

Referring now to FIG. 4D, the present invention implements a controlsystem of a vehicle 430, a WLAN interface and/or mass data storage ofthe vehicle control system. In some implementations, the presentinvention implements a powertrain control system 432 that receivesinputs from one or more sensors such as temperature sensors, pressuresensors, rotational sensors, airflow sensors and/or any other suitablesensors and/or that generates one or more output control signals such asengine operating parameters, transmission operating parameters, and/orother control signals.

The present invention may also be embodied in other control systems 440of vehicle 430. Control system 440 may likewise receive signals frominput sensors 442 and/or output control signals to one or more outputdevices 444. In some implementations, control system 440 may be part ofan anti-lock braking system (ABS), a navigation system, a telematicssystem, a vehicle telematics system, a lane departure system, anadaptive cruise control system, a vehicle entertainment system such as astereo, DVD, compact disc and the like. Still other implementations arecontemplated.

Powertrain control system 432 may communicate with mass data storage 446that stores data in a nonvolatile manner. Mass data storage 446 mayinclude optical and/or magnetic storage devices for example hard diskdrives HDD and/or DVDs. At least one HDD may have the configurationshown in FIG. 4A and/or at least one DVD may have the configurationshown in FIG. 4B. The HDD may be a mini HDD that includes one or moreplatters having a diameter that is smaller than approximately 1.8″.Powertrain control system 432 may be connected to memory 447 such asRAM, ROM, low latency nonvolatile memory such as flash memory and/orother suitable electronic data storage. Powertrain control system 432also may support connections with a WLAN via a WLAN network interface448. The control system 440 may also include mass data storage, memoryand/or a WLAN interface (all not shown).

Referring now to FIG. 4E, the present invention may be embodied in acellular phone 450 that may include a cellular antenna 451. The presentinvention may implement either or both signal processing and/or controlcircuits, which are generally identified in FIG. 4E at 452, a WLANinterface and/or mass data storage of the cellular phone 450. In someimplementations, cellular phone 450 includes a microphone 456, an audiooutput 458 such as a speaker and/or audio output jack, a display 460and/or an input device 462 such as a keypad, pointing device, voiceactuation and/or other input device. Signal processing and/or controlcircuits 452 and/or other circuits (not shown) in cellular phone 450 mayprocess data, perform coding and/or encryption, perform calculations,format data and/or perform other cellular phone functions.

Cellular phone 450 may communicate with mass data storage 464 thatstores data in a nonvolatile manner such as optical and/or magneticstorage devices for example hard disk drives HDD and/or DVDs. At leastone HDD may have the configuration shown in FIG. 4A and/or at least oneDVD may have the configuration shown in FIG. 4B. The HDD may be a miniHDD that includes one or more platters having a diameter that is smallerthan approximately 1.8″. Cellular phone 450 may be connected to memory466 such as RAM, ROM, low latency nonvolatile memory such as flashmemory and/or other suitable electronic data storage. Cellular phone 450also may support connections with a WLAN via a WLAN network interface468.

Referring now to FIG. 4F, the present invention may be embodied in a settop box 480. The present invention may implement either or both signalprocessing and/or control circuits, which are generally identified inFIG. 4F at 484, a WLAN interface and/or mass data storage of the set topbox 480. Set top box 480 receives signals from a source such as abroadband source and outputs standard and/or high definition audio/videosignals suitable for a display 488 such as a television and/or monitorand/or other video and/or audio output devices. Signal processing and/orcontrol circuits 484 and/or other circuits (not shown) of the set topbox 480 may process data, perform coding and/or encryption, performcalculations, format data and/or perform any other set top box function.

Set top box 480 may communicate with mass data storage 490 that storesdata in a nonvolatile manner. Mass data storage 490 may include opticaland/or magnetic storage devices for example hard disk drives HDD and/orDVDs. At least one HDD may have the configuration shown in FIG. 4Aand/or at least one DVD may have the configuration shown in FIG. 4B. TheHDD may be a mini HDD that includes one or more platters having adiameter that is smaller than approximately 1.8″. Set top box 480 may beconnected to memory 494 such as RAM, ROM, low latency nonvolatile memorysuch as flash memory and/or other suitable electronic data storage. Settop box 480 also may support connections with a WLAN via a WLAN networkinterface 496.

Referring now to FIG. 4G, the present invention may be embodied in amedia player 472. The present invention may implement either or bothsignal processing and/or control circuits, which are generallyidentified in FIG. 4G at 471, a WLAN interface and/or mass data storageof the media player 472. In some implementations, media player 472includes a display 476 and/or a user input 477 such as a keypad,touchpad and the like. In some implementations, media player 472 mayemploy a graphical user interface (GUI) that typically employs menus,drop down menus, icons and/or a point-and-click interface via display476 and/or user input 477. Media player 472 further includes an audiooutput 475 such as a speaker and/or audio output jack. Signal processingand/or control circuits 471 and/or other circuits (not shown) of mediaplayer 472 may process data, perform coding and/or encryption, performcalculations, format data and/or perform any other media playerfunction.

Media player 472 may communicate with mass data storage 470 that storesdata such as compressed audio and/or video content in a nonvolatilemanner. In some implementations, the compressed audio files includefiles that are compliant with MP3 format or other suitable compressedaudio and/or video formats. The mass data storage may include opticaland/or magnetic storage devices for example hard disk drives HDD and/orDVDs. At least one HDD may have the configuration shown in FIG. 4Aand/or at least one DVD may have the configuration shown in FIG. 4B. TheHDD may be a mini HDD that includes one or more platters having adiameter that is smaller than approximately 1.8″. Media player 472 maybe connected to memory 473 such as RAM, ROM, low latency nonvolatilememory such as flash memory and/or other suitable electronic datastorage. Media player 472 also may support connections with a WLAN via aWLAN network interface 474.

Referring to FIG. 4H, the present invention may be embodied in a Voiceover Internet Protocol (VoIP) phone 483 that may include an antenna 439.The present invention may implement either or both signal processingand/or control circuits, which are generally identified in FIG. 4H at482, a wireless interface and/or mass data storage of the VoIP phone483. In some implementations, VoIP phone 483 includes, in part, amicrophone 487, an audio output 489 such as a speaker and/or audiooutput jack, a display monitor 491, an input device 492 such as akeypad, pointing device, voice actuation and/or other input devices, anda Wireless Fidelity (Wi-Fi) communication module 486. Signal processingand/or control circuits 482 and/or other circuits (not shown) in VoIPphone 483 may process data, perform coding and/or encryption, performcalculations, format data and/or perform other VoIP phone functions.

VoIP phone 483 may communicate with mass data storage 502 that storesdata in a nonvolatile manner such as optical and/or magnetic storagedevices, for example hard disk drives HDD and/or DVDs. At least one HDDmay have the configuration shown in FIG. 4A and/or at least one DVD mayhave the configuration shown in FIG. 4B. The HDD may be a mini HDD thatincludes one or more platters having a diameter that is smaller thanapproximately 1.8″. VoIP phone 483 may be connected to memory 485, whichmay be a RAM, ROM, low latency nonvolatile memory such as flash memoryand/or other suitable electronic data storage. VoIP phone 483 isconfigured to establish communications link with a VoIP network (notshown) via Wi-Fi communication module 486. Still other implementationsin addition to those described above are contemplated.

It is to be understood that the exemplary embodiments described aboveare for illustrative purposes only and that various modifications orchanges in light thereof will be suggested to persons skilled in the artand are to be included within the spirit and purview of this applicationand scope of the appended claims. For example, while exemplaryembodiment 200 is described and shown as including a phased-locked loopcircuit, it is to be understood that other embodiments may use afrequency locked-loop, delay locked loop, or any other closed-loopcontrol circuitry adapted to track and filter the phase or frequency ofthe dithered clock train. Therefore, the above description should not beunderstood as limiting the scope of the invention as defined by theclaims.

1. A digital circuit comprising: a variable divider configured to dividea frequency of a clock train by a temporally-varying divider value togenerate a dithered clock train; first logic in communication with thevariable divider, the first logic configured to generate a frequencymodulation waveform based on the dithered clock train; second logic incommunication with the first logic, the second logic configured togenerate a phase modulation signal based on the frequency modulationwaveform; and a phase-value calculator in communication with the secondlogic, the phase-value calculator configured to calculate thetemporally-varying divider value based on the phase modulation signal.2. The digital circuit of claim 1, wherein the clock train comprises adigital clock train.
 3. The digital circuit of claim 1, wherein thetemporally-varying divider value comprises a fixed-divider value plus aphase value.
 4. The digital circuit of claim 3, wherein the phase valueis determined from the frequency modulation waveform.
 5. The digitalcircuit of claim 3, wherein the phase value is proportional to adeviation of the frequency modulation waveform from the center of thefrequency modulation waveform.
 6. The digital circuit of claim 1,wherein the frequency modulation waveform is periodic or quasi-periodic.7. The digital circuit of claim 1, wherein the frequency modulationwaveform comprises a triangle waveform.
 8. The digital circuit of claim1, further comprising a control circuit in communication with thevariable divider, the control circuit configured to generate aspread-spectrum clock train based on the dithered clock train.
 9. Thedigital circuit of claim 8, wherein the control circuit is configured totrack and filter the dithered clock train to generate thespread-spectrum clock train.
 10. The digital circuit of claim 8, whereinthe control circuit is configured to multiply a frequency of thedithered clock train by a fixed-multiplier value.
 11. The digitalcircuit of claim 10, wherein the temporally-varying divider valuecomprises a fixed-divider value plus a phase value, and an averagefrequency of the spread-spectrum clock train comprises a frequency ofthe clock train multiplied by the fixed-multiplier value and divided bythe fixed-divider value.
 12. The digital circuit of claim 3, wherein thephase-value calculator comprises: first and second circuit pathsconfigured to transfer the phase modulation signal to a first adder; andwherein: the second circuit path comprises a delay circuit configured totemporally delay the phase modulation signal in the second circuit pathrelative to the phase modulation signal in the first circuit path; andthe first adder is configured to generate the phase value by calculatinga difference between the phase modulation signal in the first circuitpath and the delayed phase modulation signal in the second circuit path.13. The digital circuit of claim 12, wherein the phase-value calculatorfurther comprises a second adder configured to generate thetemporally-varying divider value by adding the phase value to thefixed-divider value.
 14. The digital circuit of claim 8, wherein thecontrol circuit comprises a phase-locked loop.
 15. The digital circuitof claim 1, wherein: the second logic is further in communication withthe variable divider, and the second logic is further configured togenerate the phase modulation signal based on the frequency modulationwaveform and the dithered clock train; and the phase-value calculator isfurther in communication with the variable divider, and the phase-valuecalculator is further configured to generate the temporally-varyingdivider value based on the phase modulation signal and the ditheredclock train.
 16. A method comprising: generating a phase modulationsignal based on a frequency modulation waveform; generating a phasevalue based on the phase modulation signal; dividing a frequency of aclock train by a divider value comprising a fixed value added to thephase value to generate a dithered clock train that is phase modulatedby the phase value; and generating the frequency modulation waveformbased on the dithered clock train.
 17. The method of claim 16, whereinthe frequency modulation waveform is periodic or quasi-periodic.
 18. Themethod of claim 16, wherein the frequency modulation waveform comprisesa triangle waveform.
 19. The method of claim 16, wherein the frequencymodulation waveform comprises a digital signal.
 20. The method of claim16, wherein the clock train comprises a digital clock train.
 21. Themethod of claim 16, wherein the dithered clock train comprises a digitalclock train.
 22. The method of claim 16, wherein the phase value isproportional to a deviation of the frequency modulation waveform fromthe center of the frequency modulation waveform.
 23. The method of claim16, further comprising: tracking and locking onto the dithered clocktrain; and based on the tracking and locking steps, generating aspread-spectrum clock train that is the spread spectrum of the clocktrain.
 24. The method of claim 16, further comprising multiplying afrequency of the dithered clock train by a multiplier value.
 25. Themethod of claim 24, wherein an average frequency of a spread-spectrumclock train is a frequency of the clock train multiplied by themultiplier value divided by the fixed value.
 26. The method of claim 16,further comprising: splitting the phase modulation signal into a firstphase modulation signal and a second phase modulation signal; temporallydelaying the second phase modulation signal with respect to the firstphase modulation signal; and generating the phase value based on thedifference between the first phase modulation signal and the delayedsecond phase modulation signal.
 27. The method of claim 26, furthercomprising adding the phase value to the fixed value to generate thedivider value.
 28. A digital circuit comprising: a variable dividerconfigured to digitally modulate a width of clock pulses composing aclock train to generate a dithered clock train based on atemporally-varying divider value; first logic configured to process thedithered clock train to generate a frequency modulation waveform; secondlogic configured to process the frequency modulation waveform togenerate a phase modulation signal; and a phase-value calculatorconfigured to generate the temporally-varying divider value based on thephase modulation signal.
 29. The digital circuit of claim 28, whereinthe temporally-varying divider value comprises a fixed-divider valueplus a phase value.
 30. The digital circuit of claim 29, wherein thephase-value calculator is further configured to generate the phase valuebased on the phase modulation signal.
 31. The digital circuit of claim29, wherein the phase-value calculator is further configured to generatethe phase value by splitting the phase modulation signal into first andsecond phase modulation signals and delay the second phase modulationsignal with respect to the first modulation signal to calculate thedifference between the first phase modulation signal and the delayedsecond phase modulation signals.
 32. The digital circuit of claim 29,wherein the phase-value calculator is further configured to add thephase value to the fixed-divider value.
 33. The digital circuit of claim29, wherein the phase value is proportional to a deviation of thefrequency modulation waveform from the center of the frequencymodulation waveform.
 34. The digital circuit of claim 28, wherein thefrequency modulation waveform is periodic or quasi-periodic.
 35. Thedigital circuit of claim 28, wherein the frequency modulation waveformcomprises a triangle waveform.
 36. The digital circuit of claim 28,further comprising a control circuit configured to track and filter thedithered clock train to generate a spread-spectrum clock train.
 37. Adigital circuit for spreading the spectrum of a clock train comprising:means for generating a phase value based on a frequency modulationwaveform; means for dividing a frequency of the clock train by a dividervalue to generate a dithered clock train that is phase modulated by thephase value; means for generating the frequency modulation waveformbased on the dithered clock train; and means for tracking and lockingonto the dithered clock train to generate a spread-spectrum clock trainthat is a spread spectrum of the clock train.
 38. The digital circuit ofclaim 37, wherein the means for generating the phase value comprises:means for generating a phase modulation signal based on the frequencymodulation waveform and the dithered clock train; and means forgenerating the phase value based on the phase modulation signal and thedithered clock train.